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International Journal Of Engineering And Computer Science ISSN:2319-7242
Volume 3 Issue 9 September, 2014 Page No. 8064-8070
Wavelength Assignment in Optical WDM Optical
Network
Mudasir Ali 1,Parminder Singh Saini2
1. Department of ECE,Doaba Institute of Engineering and Technology, Punjab, India
Princeali.32@gmail.com
2. Professor in Department of ECE, Doaba Institute of Engineering and Technology, Punjab,India
Parminder.db@gmail.com
ABSTRACT
This paper analyses the wavelength assignment problem in case of WDM optical networks. The random
wavelength assignment algorithm is compared with the first – fit wavelength assignment algorithm .These
two assignment strategies are also compared with wavelength conversion case. These comparisons are made
on the basis of blocking probability, keeping the number of channels and number of links constant and the
response is calculated by varying load per link ( in erlangs). Blocking probability on a link is calculated by
using famous Erlang B formula. It is seen that blocking probability in case of random wavelength
assignment is always greater than first –fit wavelength assignment algorithm. The blocking probability in
case of WDM networks employing wavelength converters is minimum but it increases the overall cost of the
optical network.
1. INTRODUCTION
Wavelength assignment problem is one of the
important problems in optical networks as on the
first stage route of the optical network is to be
decided and after selecting the route , the
wavelength must be assigned to the route.
Wavelength division multiplexing (WDM)
technology in optical fiber networks has been
gaining a great acceptance as a means to full fill
the ever increasing bandwidth demands of
network users. WDM technology has been
improving with a steady pace since few years.
WDM systems are currently being employed in
long distance telecommunication networks on a
point to point basis , with optical signals
converted back to their electronic format at each
node.
The great challenge faced in designing
wavelength routed networks is to devise efficient
algorithms for establishing light paths in the
optical network. These algorithms must have
capability to select routes and assign wavelengths
to selected routes in such a way that uses network
resources efficiently and which increases the
number of established paths.
1.1 ROUTING AND WAVELENGTH
ASSIGNMENT
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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RWA is the unique feature of WDM networks in
which light path is implemented by selecting the
path of a physical link between source and
destination dgenodes and reserving a particular
wave length on each of these links for the light
path. Thus for establishment of an optical
connection, one must deal with these lection of the
path (Routing problem) as well as allocating the
available wave lengths forth econnections (Wave
length Assignment problem). This resulting
problem is known as routing and wave length
assignment problem [1].Wecan divide this problem
in two problems namely ;routing problem and
wavelength assignment problem and then we can
propose different solutions to this problem.
Findar out efrom the source the destination.
Assign a wavelength to the selected route.
Anend-to-end light path has to be
established prior to the communication
between any two nodes. To establish a light
path, it is required that the same wave length
be allocated on all the links along the path.
This limitationis known as the wave length
continuity constraint [2]
1.2WAVELENGTH
CONSTRAINTS
ROUTED
There are two constraints that have to be kept in
mind by the approaches when trying to solver wa.
The first
distinct wave length assignment
constrain tholds for solving wavelength
assignment problem in any wave length routing
network. These cond wave length continuity
constrain tapplies only to the simple case of wave
length routing networks that have no wave length
conversion capability inside their nodes[3].so brief
introit the miss following: A) distinct wave length
assignment constraint :all light paths sharing
common fiber must be assigned distinct wave
lengths to avoid interference. This applies ot only
with in the all-optical network but in access links
as well.
same on all the links it traverses froms ourceendnode to destination end- node[4].
1.3 WAVELENGTH
ALGORITHM
ASSIGNMENT
Wave length assignment is a unique feature
in wave length routed networks that disting
uis hes them from conventional networks.
Based on the order in which the wavelengths
researched, wavelength assignment methods
are classifiedin to most-used, first-fit ,rando
mand
Wavelength
conversion
algorithm.
Sobriefint roof wavelength assignment
algorithms are following:Random wavelength assignment [8]: In
this algorithm as et of wavelengths that can
be used to establish the connection is
determined. After that wavelength is
randomly select with uniform probability
distribution from the set.
Most- used wave length assignment
[8]: The most-used algorithm selects the
wave length most often used in the network.
The objective of this policy is to keep more
wavelengths available for calls traveling
over long paths. This algorithm requires
communication over head and storage
requirements.
Wavelength conversion wavelength
assignment [5] :Any incoming light-path can
be assigned to any wavelength on the out
put side.This eliminates wavelengthcontinuity constraints.
First-Fit wave length assignment
[7]:This algorithm numbers all wavelengths,
so that when there is ademand for
wavelengths available, those of a small
ernumberare
B) wave length continuity constraint: the wave
length assigned to each lightpath remains the
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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Considered first. The first available
wavelength is then selected. This algorithm
does not require global information system.
Its computational cost is lower because no
storage is needed to keep the network states.
It works well interms of blocking
probability and fairness so fallocation. This
algorithm is preferred for it ssmall over head
and low computational complexity. The
objective of this allocation scheme is to
minimize wavelength fragmentation [6].
2. METHODOLOGY
Our research focused on the prevention of
congestion in Wavelength division multiplexing
optical networks by developing an adaptive
dynamic natured algorithm which is tested in
Network simulator version 2 (NS2). The basic
implementation started with creation of optical
network with ten nodes and high speed links for
connectivity and communication. Research has
been divided into three phases. In the first phase
i.e. Random algorithm, the blocking probability
was much higher. Then we switched to the second
phase i.e. First fit algorithm which has lesser
blocking probability than the previous one. Finally
there is development of dynamic conversion
algorithm which has the best results out of all
three. Comparison has been done with variation of
load per links for various nodes in the network.
In this research, we have developed and
implemented a dynamic routing algorithm for
wavelength division multiplexing which use to
fetch information in early state of communication
and sort the wavelengths according to the
channels available with same frequencies on the
further nodes in optical network. Dynamic
algorithm finds the available paths with clearance
from further nodes with information of load and
availability of the same frequency as on base
node.
Figure 1.1: Simulation scenario for dynamic
routing
The simulation study has been done for dynamic
algorithm along with first fit and random routing
scheme in network simulator version 2. In
simulation setup we have considered optical
communication with ten optical nodes for
representing routing process. The base simulation
scenario for dynamic routing is shown above in
figure 1.1.
The simulation scenario for dynamic routing
contains 5 subnets and traffic start after finding
load and frequency value on all nodes. For
different nodes, we have considered blocking
probability with variation of load on nodes.
The blocking probability is good parameters for
deciding the efficiency of the optical routing
process. If the intermediate node doesn’t have
same frequency as carried by wavelength at
starting then packets will be dropped and
converters are required for conversion of the
frequency to suitable value. Below figure 1.2
shows the blocking and packet drop in simulation.
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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Figure 1.2 Simulation scenario for blocking
and packet drop
2.1ALGORITHM
FOR
DYNAMIC CONVERSION
The proposed algorithm is to reduce the cost
factor and to improve the performance of the
optical fiber network. Here the steps from 1 to 3
are for source node, step 4 is for intermediate
node , step 5 for destination node and steps 6,7 are
for control operation. The algorithm is given
below:1. Find the routes from source node having
one or more free wavelengths and list them
2. Choose first two routes R1 and R2 from the
list through shortest route algorithm and
put RP← R1 and Rs← R2.
3. Send the request RQ on R1 and R2 with the
information about destination node, route,
wavelength status for outgoing route, route
cost, load per link and route time
ii.
List the free wavelengths on route
to next node
iii.
If no free wavelength is there, then
RQ fails otherwise compare the
wavelength of RQ with the
available
wavelengths.
If
wavelength matches then XR is not
required and select that wavelength
otherwise XR will be required
iv.
Add on RQ the information about
the requirement of XR, Load and
wavelength status of outgoing
route.
v.
Forward RQ to next node
otherwise go to 6
5. Go to 4
6. do
i.
Find out the information with RQ
for R.
ii.
Calculate NR, LR, LRA, VR, XR, TR
7. Calculate Integrated route cost (CI(R)) of
route R through
CI(R) = ε(NR) + λ(LR) + ζ(LRA) + η(VR) + κ(XR)
where ε, ζ, η, κ are the parameters having value
from 0 to 1 and λ is the parameter having value to
be considered as the ratio between the rate of
wavelength converters and optical fibers.
8. Compare CI(R) of both routes and fix the
primary and backup route by using
compare algorithm.
4. If the next node is not the destination node
then
i.
Get the request RQ and find out the
information on signal
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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Choose next two routes from the list and go to (3)
till
the
list
ends
(a) Algorithm of proposed
wavelength assignment
dynamic
2.2 ALGORITHM FOR FIRST FIT
STRATEGY
 Initially number of wavelength is
calculated which is given by W = {n/k}
in given communication.
 If the wavelengths are available at
source is more than two.
Begin the process with sorting SD pairs of the
wavelength
Non Decreasing Order selection If Two or more
sequence of wavelength available Then put
highest value of wavelength as initial stage of
communication else start communication with
first available wavelength
 Path is searched for the first wavelength
selected.
 Connect the pairs for communication. If
Combination is not formed
Then discard the wavelength combination end
(b)First fit algorithm
2.3 ALGORITHM
ASSIGNMENT
FOR
RANDOM
 Store the number of wavelengths
calculated and available. Check each
possible wavelength available with cost
of wavelength.
 If the wavelengths are available at
source is more than two.
Begin the process with sorting SD pairs of the
wavelength
Random Order selection
if
Two or more sequence of same frequency
wavelength available
then
put randomly the value of wavelength as initial
stage of communication
else
start communication with first available
wavelength
 Start matching communication frequency.
If Frequency of wavelength found Then Connect
it with wavelength value Else Discard wavelength
at particular source
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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120
Blocking Probability %
 Output is W which is the number of
wavelengths.
100
80
60
40
Random
20
First Fit
Conversion
0
Number of nodes
Figure 1
Blocking Probabaility %
120
100
80
60
40
Random
20
First Fit
Conversion
0
3.
Number of nodes
Fig 2
(c)Random assignment algorithm
3. RESULTS AND DISCUSSION
Blocking Probability %
120
The following graphes clearly shows comparison
of first fit , random and conversion wavelength
assignment strategies. These show blocking
probability variation for loads 10, 20 and 30
erlangs respectively. Moreover, it is also evident
from these plots that blocking probability is
maximum in case of Random wavelength
assignment algorithm and is minimum in
wavelength conversion strategy.
100
80
60
40
Random
20
First Fit
Conversion
0
Number of nodes
Fig 3
4.CONCLUSION
Optical wavelength routed network offer huge
capacity with highs calability which makes them a
very attractive choice for then ext generation
Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
Page 8069
optical networks. The
wavelength division
multiplexing technique is considered to be one of
the best possible techniques in optical network to
enhance the capacity of optical fiber. Wave length
assignment problems are the major problems of
WDM networks. Wavelength assignmentisa
unique feature in wavelength routed networks that
distinguishes them from conventional networks.
So we analyze the performance of First-fit,
Random, Most-used and Wavelength conversion
Algorithms for wavelength assignment in WDM
unidirectional opticalring network. We compare
the blocking probability of various algorithms
with the variationinnum berof events.
ghtwaveTechnology,vol.23,no.3,
pp.955971,March2005.
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[9]AnwarAlyatama,“Wavelengthdecomposit
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probabilitiesinWDMopticalnetworkswithout
wavelengthconversions,”ComputerNetwork
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Mudasir Ali, IJECS Volume3 Issue9 September ,2014 Page No.8064-8070
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